1) Field of the Invention
The present invention relates to a method for preloading preload-adjustable rolling bearings adapted to be assembled in various precision rotary components, for example, spindle motors, rotary actuators, rotary encoders and the like for video tape recorders (VTR), hard disk drives (HDD) and laser beam printers (LBP) in order to rotatably support their rotating elements. This invention is also concerned with a method for manufacturing such preload-adjustable rolling bearings.
2) Description of the Related Art
A ball bearing is used to rotatably support a spindle of VTR or HDD while preventing whirling (i.e., motions in a direction perpendicular to the spindle) and/or axial deviations. A pair of mutually independent ball bearings (of either the deep groove type or the angular type) have heretofore been employed. With a view toward making efficient the assembly of ball bearings in a rotatably supporting part, use of a double-row ball bearing has also been proposed.
A double-row ball bearing is constructed by concentrically combining a spindle 2, which has a pair of deep inner race groove in an outer peripheral wall thereof as shown in FIG. 12(A), with an outer race 4, which has a pair of deep outer race grooves 3,3 in an inner peripheral wall thereof as depicted in FIG. 12(B), and then rotatably inserting plural balls 5,5 between the inner race grooves 1,1 and the corresponding outer race grooves 3,3 as illustrated in FIG. 12(A). FIG. 12(C) also shows retainers 6,6 for holding the balls 5,5 at equal angular intervals and seals 7,7 for preventing dust and the like from penetrating into the ball-inserted parts.
Although the construction of such a double-row ball bearing as shown in FIG. 12(C) has been known, it has heretofore been difficult to manufacture a double-row ball bearing suitable for use in supporting a spindle in VTR or HDD. This can be attributed to the reasons to be described next.
A ball bearing for use in supporting a spindle in VTR or HDD is required to have extremely high accuracy in order to avoid whirling motions and axial displacements. Therefore, a ball bearing for use in supporting such a spindle is used in a state preloaded in an axial direction.
Upon insertion of the balls 5 between each inner race groove 1 and its corresponding outer race groove 3 to assemble the deep-groove ball bearing, on the other hand, the inner race groove 1 and the outer race groove 3 are brought into an eccentric relationship to widen a radial spacing 8, which extends in a circumferential direction between both the grooves 1 and 3, at a part thereof as illustrated in FIG. 13. From the widened part of the spacing 8, the balls 5,5 are inserted between the inner race groove 1 and the outer race groove 3 as many as desired. Thereafter, the inner race groove 1 and the outer race groove 3 are rendered concentric with each other and the desired number of the balls 5,5 are disposed at equal angular intervals.
To rearrange the plural balls 5,5, which have been inserted together in the widened part of the spacing 8, at equal angular intervals as described above, it is necessary to make the individual balls 5,5 slide on and relative to the inner race groove 1 and the outer race groove 3. If the individual balls 5,5 are strongly pressed by the inner race groove 1 and the outer race groove 3, in other words, are in a preloaded state at this time, rolling surfaces of the inner race groove 1, outer race groove 3 and balls 5,5 are prone to damage. Their damage leads to such a problem such that vibrations may occur during rotation or the durability may be impaired.
In the case of the construction that a pair of single-row deep ball bearings are arranged at an interval as disclosed, for example, in Japanese Patent Application Laid-Open (Kokai) No. SHO 57-200722, on the other hand, each ball bearing is assembled in a state not applied with a preload so that this construction is free of such inconvenience as referred to above. However, the assembly work of the ball bearings is cumbersome.
Further, double-row, deep-groove ball bearings useful in tension pulleys or water pumps are disclosed, for example, in Japanese Patent Application Laid-Open (Kokai) Nos. SHO 61-65913 and SHO 61-79899 and Japanese Utility Model Application Laid-Open (Kokai) Nos. SHO 50-101753 and SHO 56-127456. These bearings are however not require to have very high rotational accuracy and are used in a state not applied with preload. They cannot therefore be used to support spindles in VTR, HDD or the like.
Japanese Patent Application Laid-Open (Kokai) No. SHO 61-145761 discloses a double-row angular ball bearing while Japanese Utility Model Application Laid-Open (Kokai) No. SHO 62-22323 discloses a double-row ball bearing constructed in combination of a deep-groove ball bearing and an angular ball bearing. To assemble an angular ball bearing, it is necessary to heat an outer race as disclosed, for example, in Japanese Utility Model Publication (Kokoku) No. SHO 39-3916 so that the outer race is caused to expand to protect shoulder portions of each groove and/or rolling surfaces of balls when the balls pass along the shoulder portions. The assembly work is therefore irksome.
Japanese Patent Application Laid-Open (Kokai) No. SHO 57-140912 discloses the invention in which after a double-row, deep-groove ball bearing equipped with an outer race formed in combination of a main outer race and a subordinate outer race axially displaceable relative to the main outer race has been assembled in a state not applied with preload, the subordinate outer race is caused to displace axially to apply a predetermined preload and is then fixed by a presser member. It also discloses the invention in which a predetermined preload is applied by axially pressing the subordinate outer race with a spring. The inventions disclosed in this patent publication, however, requires such a presser member or spring. This results in more cumbersome management or control of parts and also in more irksome assembly work. Moreover, the ball bearing may require an unduly large axial length.
U.S. Pat. No. 4,900,958 discloses such constructions as shown in FIGS. 14 and 15, respectively. In the case of the construction depicted in FIG. 14, ball bearings 9,9 of the deep groove type (or of the angular type) are disposed in a pair between an outer peripheral wall of a spindle 2 and an inner peripheral wall of a housing 10, and inner races 11,11 of both the ball bearings 9,9 are pushed in a direction approaching toward each other to apply a preload to balls 5,5 of both the ball bearings 9.9.
Described specifically, an end face of one of the inner races, i.e., of the inner race 11 located on the right-hand side as viewed in FIG. 14 is brought into abutment against a stop ring 12 and the other inner race, i.e., the inner race 11 on the left-hand side as viewed in FIG. 14 is pushed toward the stop ring 12, whereby a preload is applied. The left-hand inner race 11 is fixed on the spindle 2 by an adhesive or shrinkage fitting. It is therefore necessary to continuously push the left-hand inner race 11 toward the stop ring 12 under a load equivalent to the preload until the adhesive solidifies or the left-hand inner race so heated shrinks.
In the case of the construction illustrated in FIG. 15, on the other hand, inner race grooves 1,1 are formed in double rows in an outer peripheral wall of a spindle 2. A spacer 13 is arranged between outer rings 4,4 which are internally fitted in a pair in a housing 10. By the spacer 13, both the outer races 4,4 are pushed in a direction moving away from each other so that a preload is applied to balls 5,5.
Further, Japanese Utility Model Application Laid-Open (Kokai) No. HEI 3-36517 discloses such a construction as shown in FIG. 16. By a leaf spring 14 held between outer races 4,4 arranged in a pair, the outer races 4,4 are both pushed in a direction moving away from each other so that a preload is applied to balls 5,5.
Japanese Patent Application Laid-Open (Kokai) No. HEI 3-222661 and U.S. Pat. No. 5,045,738 disclose such constructions as illustrated in FIGS. 17 and 18, respectively. In the construction of FIG. 17, a preload is applied by pushing with a leaf spring 14 an outer race 4 internally fitted in a housing. In the construction of FIG. 18, on the other hand, an outer race 4 is fixed on the housing 10 by an adhesive or shrinkage fitting while applying a predetermined preload. Of double-row outer race grooves 3,3, one of the outer race groove 3,3 is formed in an inner peripheral wall of the outer race 4 while the other outer race groove 3 is formed in an inner peripheral wall of the housing.
Although illustration by drawings is omitted, Japanese Patent Application Laid-Open (Kokai) No. SHO 61-145761 and U.S. Pat. No. 4,713,704 discloses such a construction that one of double-row inner race grooves is formed in an outer peripheral wall of a spindle, the other inner race groove is formed in an outer peripheral wall of an inner race externally fitted on the spindle, and the inner race is adhered and fixed to the spindle with balls being applied with an appropriate preload.
The above-described constructions of FIGS. 14 to 18 and that disclosed in Japanese Patent Application Laid-Open (Kokai) No. SHO 61-145761 are accompanied not only by the problems that they require cumbersome assembly work and parts management or control as described above but also by the problem that they tend to develop small vibrations. In each of the above-described conventional constructions, each inner race 11 or outer race 4 tends to tilt upon preloading although the extent of the tilting may not be very large, because the inner race 11 is loosely fitted on the spindle 2 (in the case of the construction shown in FIG. 14) or the outer race 4 is loosely fitted in the housing (in the case of the constructions illustrated in FIGS. 15 to 18, respectively). When tilted, the bearing so assembled produces small vibrations during rotation, leading the potential problem that the performance of HDD or the like with the bearing assembled therein may be reduced.
Further, the work to fix the inner race 11 on the spindle 2 or the outer race 4 on the housing 10 by an adhesive or shrinkage fitting is conducted in a factory where the rolling bearing is manufactured. As a corollary to this, the assembler (user) who purchases the bearing and assembles it in HDD or the like cannot change the preload of the bearing. It is therefore the current circumstance that the bearing is used as purchased without adjustment of its preload even when the assembler wishes to adjust the preload in view of a difference in specification.
To allow HDD or the like to exhibit its best performance, it is preferred to adjust the preload of the bearing in accordance with the manner of its use.
Japanese Patent Application Laid-Open (Kokai) No. HEI 1-266320 discloses a construction which permits adjustment of the preload. Namely, outer races of a rolling bearing are pushed by a piezoelectric actuator in a direction moving away from each other so that a preload is applied to the rolling bearing. The preload is adjustable by controlling a voltage impressed to the piezoelectric actuator. The construction disclosed in this patent publication, however, cannot avoid an overall dimensional increase of the rolling bearing. The rolling bearing so manufactured may be assembled in a large apparatus such as a machine tool, but its assembly in a small apparatus like HDD is difficult.